This invention relates generally to fasteners, and more particularly relates to a novel and improved anchor bolt which is so constructed and arranged as to be capable of being driven into anchored engagement with the surrounding wall of a bolt hole, including a visual indicator to show that the expandible members of the bolt have been properly expanded for engagement.
A myriad of anchor bolts have been designed for fastening objects to relatively thick, tough construction materials such as concrete or rock which are positioned so that it is impossible or impractical to thread a nut onto the leading end of a bolt on the opposite side of the construction material from that on which the object is to be fastened. The usual method of anchoring a bolt in a hole, such as in concrete, is to devise some means for inducing frictional engagement between the anchor bolt and the wall of the hole. Most integral anchor bolts have been devised as an alternative to the common combination of an expandible sleeve inserted initially into a hole of somewhat larger diameter than the bolt hole in the object to be anchored and a lag screw with an outside diameter slightly larger than the inside diameter of the sleeve such that when the lag screw is screwed into the sleeve, the sleeve is forced to expand into frictional engagement with the walls of the hole.
Another general category of prior art anchor bolts includes anchor bolts with expandible sleeves that are positively expanded into engagement with the walls of the hole by longitudinal squeezing or wedging forces applied on the sleeves by tightening the nuts on the anchor bolts, such as the device disclosed in my U.S. Pat. No. 3,339,449. While the combination bolt and sleeve devices are effective for their intended purposes, it is not always possible or desirable to provide a hole in the anchoring material which is larger in diameter than the object to be anchored. To alleviate this problem, another category of anchor bolts has been devised which includes wedge members located in circumferential grooves or recesses on the bolt shanks which can be expanded into engagement with the walls of a hole. Usually these anchor bolts depend upon some initial engagement of the wedge device with the wall of the hole whereby further outwardly directed drag on the shank caused by tightening down on the bolt in combination with resistance to the drag due to the initial engagement results in further expansion of the wedge members into tighter engagement with the walls of the hole. Typical of this category of anchor bolts are U.S. Pat. Nos. 3,215,027 issued to H. J. Modrey et al., 3,427,919 issued to L. Lerich, 3,456,551 issued to M. Ishihara, 3,546,998 issued to L. Lerich, 3,703,119 issued to L. Lerich, and 3,744,367 issued to L. Lerich. Continuing problems with obtaining initial engagement of the wedge member with the walls of the hole and the uncertainty associated therewith has led to the development of another variation of the anchor bolt including wedge members in circumferential recessed grooves which are positively actuated or expanded by tightening of a nut on the anchor bolt without depending on initial engagement with the walls of the hole. Examples of this latter group of devices include U.S. Pat. Nos. 2,896,494 issued to L. Lerick, 3,107,569 issued to L. Lerick, and 3,352,193 L. Lerich.
Even though the latter type of device with the positive nut actuated expansion wedges is somewhat more certain of engagement with the walls of the hole, none of the prior art devices provide any method of visually determining whether the wedge members have actually been expanded to their proper position into engagement with the walls of the hole. Further, many times it is somewhat tedious and sometimes virtually impractical to turn the nut or the anchor bolt itself in order to draw the wedge members into engagement with the walls of the hole.